The invention relates to a data carrier, in particular a smart card, having at least one transmitting/receiving antenna and also a rectifier circuit connected downstream thereof and serving for providing a supply voltage for at least one circuit unit. A voltage regulator is connected in parallel with the supply voltage terminals of the circuit unit(s).
Such a data carrier is disclosed in International Patent Disclosure WO 97/08651. The known data carrier is a combined smart card whose internal electronic circuits can be operated both via a contact bank and via an integrated coil. In contactless operation via the antenna coil, the energy required to operate the internal circuits is supplied by the electromagnetic field received by the coil. In this case, the available energy fluctuates to a very great extent, since it essentially depends on the distance between the data carrier or the smart card and a read/write station supplying the energy.
This represents a problem since the required energy must be available at any time for desired functioning of the data carrier. Well developed circuits stop functioning before the energy supply deteriorates to such an extent that malfunctions can occur.
The circuits of a contactless data carrier are usually configured in such a way that, at a required maximum range, they manage with the power offered. However, with a shorter distance between the data carrier or the smart card and the read/write station, an excess power is then available which is taken up by the parallel voltage regulator and is thus needlessly lost.
It is accordingly an object of the invention to provide a data carrier with regulation of the power consumption which overcomes the above-mentioned disadvantages of the prior art devices of this general type, which is matched as optimally as possible to the present supply of power.
With the foregoing and other objects in view there is provided, in accordance with the invention, a data carrier in particular a smart card. The data carrier contains at least one transmitting/receiving antenna, at least one circuit unit having supply voltage terminals, a rectifier circuit connected downstream of the at least one transmitting/receiving antenna and serving for providing a supply voltage for the at least one circuit unit, and a voltage regulating circuit connected in parallel with the supply voltage terminals of the at least one circuit unit and connected to the rectifier circuit. The voltage regulating circuit has an output at which a signal proportional to a regulating signal of the voltage regulating circuit can be tapped off. A controllable clock signal generator is provided and has a control input connected to the output of the voltage regulating circuit. The controllable clock signal generator is connected to the at least one circuit unit and outputs a clock signal received by the at least one circuit unit.
In accordance with an added feature of the invention, the voltage regulating circuit contains a first transistor connected between the supply voltage terminals, and a second transistor connected to one of the supply voltage terminals and has an output terminal. The first transistor forms with the second transistor a current mirror circuit having an output terminal connected to the control input of the controllable clock signal generator. The output terminal of the current mirror is the output terminal of the second transistor.
In the case of the data carrier according to the invention, the object is achieved in that the voltage regulating circuit has an output at which a signal proportional to the regulating signal of the voltage regulating circuit can be tapped off, and in that the output is connected to the control input of a controllable clock signal generator, which provides the clock signal for the at least one circuit unit.
The invention is based on the insight that the power consumption of electrical or electronic circuits depends on the clock frequency and, in particular, increases as the clock frequency increases. In a manner according to the invention, the clock signal generator is configured to be controllable, so that the frequency of the clock signal can be altered by a control signal. The control signal is obtained from the regulating signal of the parallel regulator. In particular, a signal that is proportional to the excess current is used as a measure for the control of the clock signal frequency. This can advantageously be done by a current mirror circuit. In an advantageous embodiment of the invention, the clock signal generator is realized as a voltage-controlled oscillator. Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a data carrier with regulation of the power consumption, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.